Borehole Acoustic Beam Collimation via Non-Linear Mixing
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Solution Overview
Problem
Conventional acoustic sources in boreholes face limitations in generating a collimated acoustic beam in the 10 kHz-100 kHz range due to constraints such as large beam spread, low bandwidth, and difficulty in achieving collimation, especially in the borehole environment where conditions like long source arrays and uniform coupling to rock formations are not feasible.
Innovation Solution
A method involving the generation of first and second acoustic waves by transducers within a borehole, which are then mixed in a non-linear medium to produce a collimated beam, and further refined using a diverging acoustic lens to compensate for borehole curvature, allowing for a compact device to direct the beam into rock formations and other materials around the borehole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional low-frequency transducers are used, then the frequency range 10 kHz-100 kHz can be accessed, but the beam spread becomes very large and collimation cannot be achieved
Solution Approach 1:
The acoustic source is segmented into multiple transducers arranged in an array, where each transducer operates at a higher frequency (e.g., 250 kHz to 1.5 MHz) but the collective array produces a lower frequency collimated beam through constructive interference and phase control
Solution Approach 2:
The invention transitions from single transducer operation to multi-dimensional array processing, using spatial arrangement and phase control across multiple elements to achieve collimation that cannot be obtained with a single low-frequency transducer
2Shape
If a long source array is used to achieve collimation, then beam directionality improves, but the device complexity and difficulty of uniform coupling to rock formation increase
Solution Approach 1:
The invention changes the operating parameters by using higher frequency transducers (250 kHz to 1.5 MHz) in an array configuration, which allows achieving collimation with a more compact and manageable array length compared to using lower frequency single transducers
Solution Approach 2:
The transducer array serves multiple functions: it generates higher frequency acoustic waves, controls beam direction through phase adjustment, and achieves collimation without requiring extremely long array lengths or complex coupling mechanisms
3Shape
If high frequency signals are used, then beam collimation can be achieved, but the penetration distance becomes relatively short
Solution Approach 1:
The invention uses periodic modulation of multiple high frequency signals to generate a lower frequency difference signal that maintains collimation properties while extending penetration distance, effectively combining benefits of both high and low frequency operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the generation of a collimated acoustic beam with low frequency and broad bandwidth, effectively overcoming the limitations of conventional sources by maintaining beam collimation and improving imaging capabilities of rock formations and materials surrounding the borehole.
Implementation Method 1
the composition of the non-linear medium produces a collimated beam by a non-linear mixing of the first and second acoustic waves
Implementation Method 2
transmitting the collimated beam through a diverging acoustic lens to compensate for a refractive effect caused by the curvature of the borehole
Data Source
AI summary
In some aspects of the invention, a method of generating a beam of acoustic energy in a borehole is disclosed. The method includes generating a first acoustic wave at a first frequency; generating a second acoustic wave at a second frequency different than the first frequency, wherein the first acoustic wave and second acoustic wave are generated by at least one transducer carried by a tool located within the borehole; transmitting the first and the second acoustic waves into an acoustically non-linear medium, wherein the composition of the non-linear medium produces a collimated beam by a non-linear mixing of the first and second acoustic waves, wherein the collimated beam has a frequency based upon a difference between the first frequency and the second frequency; and transmitting the collimated beam through a diverging acoustic lens to compensate for a refractive effect caused by the curvature of the borehole.